Pemberian lactobacillus reuteri DSM 17938 pada bayi prematur di rumah sakit Dr. Cipto Mangunkusumo: kajian terhadap kejadian enterokolitis nekrotikans = Oral administration of lactobacillus reuteri DSM 17938 in preterm infants at Dr. Cipto Mangunkusumo hospital: a study towards the prevalence of necrotizing enterocolitis